The goal of this proposal is to evaluate a novel role for Prdx6 in the activation of NADPH oxidase (NOX2). Our hypothesis is that in response to a stimulus, Prdx6 is phosphorylated and translocates to the plasma membrane where it generates lysophosphatidylcholine (lysoPC) resulting in activation of NOX2. This hypothesis will be tested by 3 (of 5) specific aims. Specific Aim 1 will evaluate the effect of Prdx6 knockout on agonist-induced activation of NOX2 in alveolar macrophages (AM) and pulmonary microvascular endothelial cells in culture and in the isolated perfused lung. Activation is determined by translocation of cytosolic components to the membrane and generation of reactive oxygen species (ROS). Specific Aim 2 will evaluate the mechanism for Prdx6-mediated activation of NOX2; we propose that generation of lysoPC by the phospholipase A2 (PLA2) activity of Prdx6 is responsible. Specific Aim 3 will evaluate the requirement for Prdx6 phosphorylation in its translocation to the plasma membrane and NOX2 activation. We further propose that binding of one of the cytosolic components (p67phox) to Prdx6 inhibits its PLA2 activity and abrogates the NOX2-activation signal. Specific Aim 4 will study the interaction of Prdx6 with p67phox in intact cells and with recombinant protein in vitro with specific focus on the PLA2 activity of Prdx6 and the kinetics of the protein-protein interaction. Finally, Specific Aim 5 will investigate the effect of a Prdx6 PLA2 inhibitor, MJ33, in preventing oxidative stress with ischemia in the isolated lung and acute lung injury with ischemia-reperfusion in vivo. We postulate that this agent will maintain the protective peroxidase activity of Prdx6 while inhibiting the activation of NOX2. The proposed studies will provide a coordinated effort to investigate this novel role of Prdx6 and will provide the basic insights for development of new methods to inhibit the activation of the NOX2 enzyme complex and ameliorate ROS-mediated lung injury.